1. Field of the Invention
The invention relates to alloys for use in light water nuclear reactor (LWR) core structural components and fuel cladding.
2. Description of the Prior Art
Zirconium alloys, particularly those commonly known as Zircaloy 2 and Zircaloy 4, are used in light water reactor cores because of their relatively small capture cross-section for thermal neutrons. The addition of 0.5 to 2.0 percent by weight niobium and up to 0.25 percent of a third alloying element to these zirconium alloys for purposes of corrosion resistance in the reactor core is suggested in U.S. Pat. No. 4,649,023 as part of a teaching of producing a microstructure of homogeneously dispersed fine precipitates of less than about 800 angstroms. The third alloying element is a constituent such as iron, chromium, molybdenum, vanadium, copper, nickel and tungsten.
Pellet-clad interaction (PCI) resistance is sought in U.S. Pat. Nos. 4,675,153 and 4,664,881 by use of zirconium based alloys including "zirconium-2.5 w/o niobium". The latter teaching also refers to "Zr-Nb alloys containing about 1.0 to 3.0 w/o Nb". In these patents, oxygen is present "below about 350 ppm of said alloy".
U.S. Pat. No. 4,648,912 teaches improving high temperature corrosion resistance of an alpha zirconium alloy body by rapidly scanning the surface of the body with a laser beam. The alloys treated included zirconium-niobium alloys.
It has been found by various investigators in the prior art literature that the addition of niobium to a zirconium alloy for use in light water reactors will reduce hydrogen uptake from waterside corrosion, stabilize oxygen-irradiation defect complexes and make the alloy more resistant to annealing of irradiation damage. It is also reported by investigators that niobium will enhance work hardenability of irradiated Zircaloy but that an addition of niobium above the 1 percent level will not result in further additional benefit in mechanical properties.